Anti-icing systems are widely used for the prevention of ice buildup on leading edges of aircraft structures. Components such as wings, leading edge slats and spoilers, engine inlets, engine struts, radar domes, and vertical and horizontal stabilizers are fitted with anti-icing equipment and systems as appropriate for the particular aircraft.
Known thermal anti-icing systems typically include a complex variety of installation details, including hot air distribution tubes, pipes, and plates, brackets, stiffeners, fasteners, welds, or adhesive bonds. These details increase engineering and manufacturing costs, and also increase the operating and maintenance costs for aircraft. Also, the extra weight of such complex structures imposes a performance penalty, i.e., increases aircraft fuel consumption. Further, the complex configuration leads to inefficient pressure losses in air supply lines and ducts. Also, in many configurations, the warmest air does not reach areas required to be heated without excessive mixing and cooling, thus reducing efficiency
A number of de-icing systems have been identified. These are described in the patent literature as follows:
U.S. Pat. No. 2,447,095 issued to Schmidt on Aug. 17, 1948, discloses an airplane anti-icing system having an interior air distribution plenum (or, alternatively, hot air "spray tubes") and a perforated air distribution plate to evenly direct hot de-icing air from the plenum toward the interior surface of aircraft leading edge surfaces.
U.S. Pat. No. 2,470,128 issued to Barrick on May 17, 1949, discloses a leading edge construction technique which superficially resembles the novel anti-icing apparatus disclosed herein to a limited extent. The patented technique utilizes multiple corrugated sections, including a nose portion and an interior box beam portion, with communicating passageways between the sections, as illustrated for example in FIG. 2 of Barrick. The corrugated members are preformed. Techniques for securing the skin member to the corrugated member are not disclosed.
U.S. Pat. No. 2,478,878 issued to Smith et al. on Aug. 19, 1949, discloses a thermal anti-icing structure for incorporation into the leading edge structures of airplane wings. The structure provides an undersheet beneath the skin, with fasteners configured to provide a space between the undersheet and the skin. Also, a plurality of strips are provided for fitting between the undersheet and the skin, so as to define warming spaces for reception of heating air. It can be seen that the structure of Smith's invention requires many parts, thus necessitating extensive engineering and manufacturing labor.
U.S. Pat. No. 2,556,736, issued to Palmatier on June 12, 1951, discloses a de-icing system for rotor blades of helicopters and similar structures. The structure utilizes a spaced air flow passageway configuration which is positioned by a multitude of fasteners and support brackets, as may be seen in FIG. 2, FIG. 3, or FIG. 5 of Palmatier. Conventional bracket and fastener construction is utilized, thus increasing the complexity, cost, and weight of the Palmatier design when compared to the present invention.
U.S. Pat. No. 2,581,760, issued to Harpoothian et al. on Jan. 8, 1952, shows a stressed skin thermal de-icing design. The design includes inner and outer skins, with chordwise corrugations for directing hot air flow. The corrugated structure and the inner and outer skins are joined by rows of spaced fastening elements. This design thus contains the added weight of a multitude of fasteners and brackets. Also, the pressure losses and leaks inherent in such design result in reduced efficiency when compared to the present invention.
U.S. Pat. No. 2,638,170, issued to Prewitt on May 12, 1953, shows a de-icing design for a helicopter rotor or an aircraft propeller. The airfoil leading edge member has a hollow interior with a generally triangular shaped section, and the member is formed from a single integral tube by drawing. The rear of the leading edge member is perforated and adapted to supply warmed air. The warmed air heats the rotor for de-icing; and, as the air is cooled, it is swept toward the tip of the rotor where it is discharged.
U.S. Pat. No. 2,723,092, issued to Paselk et al. on Nov. 8, 1955, shows an anti-icing radome design. The structure provides anti-icing fluid passageways adjacent to the external walls, and utilizes laminated glass fiber construction.
U.S. Pat. No. 3,023,860, issued to Ellzey on Mar. 6, 1962, provides passageways for anti-icing air in the interior of an airfoil section The passageways are formed by a spiral winding construction technique Closed segments between passageways are welded such as by electrical spot welding.
As will be explained hereinafter, expansion of an appropriate sheet metal is a favored technique for producing important components of the novel de-icing systems disclosed herein. Various techniques are known for expanding materials into controlled shapes. One method is illustrated in U.S. Pat. No. 2,690,002 issued to Grenell on Sept. 28, 1954. Grenell shows how structural members requiring one flat surface, or heat exchangers requiring a plurality of interconnecting passages, may be constructed utilizing pressurized expansion. In Grenell, sheets are joined by sealing the edges of the sheets by welding, and by joining the faces of the sheets by spot welding. The joined sheets are then heated and hot rolled; and these steps are followed by cooling, cold rolling, and annealing. Grenell shows how heat exchange passages are created by hydraulic expansion, which may be controlled (i.e., by use of dies), or by free expansion where pressurization of the parts is adjusted to limit the amount of metal expansion.
Another method for forming passageways in expanded multi-layer metal parts is described in an article entitled "Controlled-Disbond Cladding Adds New Dimension To Metalworking," by Daniel V. Edson, appearing in Design News, June 16, 1986. The article describes a technique developed by Texas Instruments Incorporated for fabricating passageways between bonded metal sheets. The technique bonds sheets of metal together via roll bond cladding, and includes a step of printing a temperature sensitive ink between metal layers at those locations where it is desired to form passageways. Upon heating, the ink decomposes, generating a gas which provides pressure necessary to expand the portions of the metal sheets adjacent to the inked surfaces.
It is significant that none of the prior art patents identified above are concerned with the specific problems of metal fatigue or corrosion which are of paramount importance in, particularly, modern, large capacity, passenger aircraft, for example. Nor do they disclose devices which would inherently reduce stresses and metal fatigue so as to increase safe life of aircraft components or to reduce maintenance. Neither have prior art devices addressed anti-icing aircraft structures with a minimum of internal components and fasteners so as to reduce aircraft empty weight. Furthermore, the devices disclosed in many of the prior patents are considerably more complex than we consider desirable, especially from a manufacturing or maintenance standpoint.